ASME B36.19M (stainless steel pipe) · DN 450
Outside diameter 18.000" (457.20 mm), wall 0.188" (4.78 mm), inside diameter 17.624" (447.64 mm).
| Trade size | NPS 18 · DN 450 |
|---|---|
| Schedule | Schedule 10S |
| Standard | ASME B36.19M (stainless steel pipe) |
| Outside diameter | 18.000" · 457.20 mm · designated 457 mm in the metric column |
| Wall thickness | 0.188" · 4.78 mm |
| Inside diameter | 17.624" · 447.64 mm |
| Weight, plain end | not published |
NPS 18 schedule 10s pipe measures 18.000 in (457.20 mm) across the outside with a 0.188 in wall, so the bore is 17.624 in (447.64 mm). That bore gives a flow area of 243.9 in² and holds 12.67 US gallons per foot (157.4 litres per metre). The outside diameter is 95.7 times the wall, and the steel itself has a cross-section of 10.52 in². One trade size up, NPS 20 in the same schedule carries 1.23 times the flow area.
Schedule 5 is the next lighter wall at NPS 18: 0.165 in, 0.023 in thinner, which opens the bore to 17.670 in and adds 0.5% to the flow area.
Schedule 10 is the next heavier wall at NPS 18: 0.250 in, 0.062 in thicker, which narrows the bore to 17.500 in and cuts 1.4% from the flow area.
Next trade size up in this schedule: NPS 20 schedule 10s, bore 19.564 in.
| Flow area | 243.9 in² |
|---|---|
| Capacity | 12.67 US gal/ft · 157.4 L/m |
| Metal area | 10.52 in² |
| Moment of inertia | 417.3 in⁴ |
| Section modulus | 46.36 in³ |
| Radius of gyration | 6.298 in |
| Outside surface | 4.712 ft² per foot |
Plain geometry of a hollow circle with OD = 18.000 in and ID = 17.624 in: flow area π/4·ID², metal area π/4·(OD² − ID²), moment of inertia π/64·(OD⁴ − ID⁴), section modulus I ÷ (OD/2), radius of gyration √(I ÷ metal area), capacity flow area × 12 ÷ 231 (231 in³ to the US gallon). Nominal dimensions, so mill tolerance and corrosion allowance are not included.
Nominal Pipe Size is a label, not a measurement. NPS 18 pipe has an outside diameter of 18.000 inches, and it keeps that outside diameter in every schedule made. What the schedule number changes is the wall: at schedule 10s the wall is 0.188 inches, so the bore comes out at 17.624 inches.
That is the practical consequence. Fittings, flanges, supports and threading dies are sized to the outside diameter, so they fit any schedule of the same trade size. Flow, pressure drop and anything that has to pass through the pipe depend on the inside diameter, which changes with every schedule. Order by trade size and schedule; work your hydraulics from the bore.
Same outside diameter of 18.000 inches throughout - only the wall and the bore move.
| Schedule | Wall (in) | ID (in) | Weight (lb/ft) |
|---|---|---|---|
| Schedule 5 · 5S | 0.165 | 17.670 | 31.46 |
| Schedule 10 | 0.250 | 17.500 | 47.44 |
| Schedule 20 | 0.312 | 17.376 | 58.94 |
| Schedule 30 | 0.438 | 17.124 | 82.23 |
| Schedule 40 | 0.562 | 16.876 | 104.67 |
| Schedule 60 | 0.750 | 16.500 | 138.30 |
| Schedule 80 | 0.938 | 16.124 | 171.08 |
| Schedule 100 | 1.156 | 15.688 | 208.15 |
| Schedule 120 | 1.375 | 15.250 | 244.37 |
| Schedule 140 | 1.562 | 14.876 | 274.48 |
| Schedule 160 | 1.781 | 14.438 | 308.79 |
| Standard wall (STD) · 40S | 0.375 | 17.250 | 70.65 |
| Extra strong (XS) · 80S | 0.500 | 17.000 | 93.54 |
0.188 inches (4.78 mm). The outside diameter is 18.000 inches (457.20 mm) whatever the schedule, so this wall leaves an inside diameter of 17.624 inches.
17.624 inches (447.64 mm). Inside diameter is outside diameter minus twice the wall: 18.000 - 2 x 0.188 = 17.624 inches.
No. NPS 18 is a trade size, not a measurement. The pipe measures 18.000 inches across the outside and 17.624 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
This table runs from NPS 1/8 to NPS 24 and stops there. ASME B36.10M itself continues to NPS 80; those larger sizes are not carried here, so a size above NPS 24 is missing rather than undefined.
Dimensions are as defined by ASME B36.19M (stainless steel pipe). This site is an independent reference and is not affiliated with, endorsed by or approved by any standards body.
Every value on this page was cross-checked against 3 independent published sources:
Sources disagree here. Published tables split on the last digit here - 4.78 mm (b3610m-wermac), 4.775 mm (b3610m-wikipedia). The figure printed is 0.188 in (4.78 mm), carried by the majority of the sources. The two readings describe the same wall: they differ by less than a thousandth of an inch, far inside the mill tolerance of minus 12.5 percent on wall thickness.
Last-digit inch walls across the whole table: 0.594, 0.688, 0.719, 0.844, 0.938, 1.094, 1.219, 1.438, 1.969, 2.344 in (b3610m-fbc) against 0.593, 0.687, 0.718, 0.843, 0.937, 1.093, 1.218, 1.437, 1.968, 2.343 in (b3610m-wikipedia). Two families of inch figures are in circulation, one a thousandth of an inch below the other, and they come from rounding the millimetre wall the standard tabulates rather than from any difference in the pipe. The higher family is what the majority of the sources read here carry and is what this site prints; the affected rows say so individually. Nothing turns on the choice: the wall tolerance is minus 12.5 percent, which at a half-inch wall is sixty times the gap.
NPS 14 extra strong (XS): 0.469 in (b3610m-fbc) against 0.500 in (b3610m-etb) against 0.500 in (b3610m-wikipedia). 0.500 in is printed here. Two of the three inch sources give it, both millimetre sources give 12.70 mm which is 0.500 in, and extra strong is a 0.500 in wall at every size from NPS 12 up. The 0.469 in reading looks like a misplaced row in that one chart, but it is recorded rather than deleted.
Nearby sizes